1. Field of the Invention
The present invention relates to a case, particularly for single- or multi-stage pumps with centrifugal radial impeller, which comprises, for each stage and for each impeller, a device for diffusing and directing the flow delivered by the impeller. The invention furthermore relates to a method for the manufacture of said case with metal plate.
2. Description of the Prior Art
Italian patent Application No. 85605 A/89 filed on June 7, 1989 in the name of the same Applicant discloses a centrifugal pump incorporating an ejector, which ejector comprises a directing device with at least one approximately radial channel having an annular outlet section which extends peripherally to the diffusion duct of the ejector.
By means of said directing device, the flow delivered from the impeller is directed toward a central portion of the case adjacent to the outer wall of the diffusion duct, at such a distance from the discharge outlet to promote separation of the air and its conveyance toward the delivery port.
Though said known pump has the above described advantages, in a preferred embodiment it entails the use of a diffuser which, as is known, has the function of converting the kinetic energy imparted to the fluid by the impeller into pressure energy with the best possible efficiency.
As is known, diffusers are elements designed to operate in optimum operating conditions beyond which efficiency is lowered considerably.
It should be furthermore added that said elements have a relatively complex bladed structure requiring accurate design and rather onerous conventional machining which severely affects the overall cost of the pump.